2 Claims. (Cl. 75206) ABSTRACT OF THE DISCLOSURE Aluminum is alloyed with a dispersion-modified irongroup metal or alloy having dispersed uniformly therein a particulate metal oxide having a free energy of formation (AF) at 1000 C., of at least 104 kilocalories per gram atom of oxygen and an average particle size in the range of 5 to 100 millimicrons. About 0.05 to by volume of a particulate metal oxide having a AP at '1000 C. of at least 104 kilocalories per gram atom of oxygen is dispersed in particulate aluminum. A minor proportion of said oxide-containing aluminum is mixed with a major proportion of particulate dispersion-modified iron-group metal or alloy and the mixture is alloyed.

In describing this invention the term iron-group metals is intended to include the metals iron, cobalt and nickel. The term alloys of iron group metals is intended to include alloys .inwhich one of the-iron-group metals comprises at least 50%-by weight of the alloy. 1

Heretofore, alloys comprising-a matrix of nickel and at least one otheralloying metal, in which alloys there is dispersed a refractory oxide, have, in general, been prepared by blending powders of the alloying metal with the dispersion-modified nickel or nickel-base alloy, and there after cnnsolidating and working the 'blendedrnetal powders to effect alloyingand to'produce a consolidated billet to be subsequently further-worked. Withsome metals, this method has given reasonably satisfactory results; in other cases a high degree of porosity develops when the compacted powder billet is heat-treated prior to hot or cold working. This porosity has been especially evident where nickel-base dispersion-modified metal powders have been combined with powdered aluminum with the object of preparing a dispersion-modified nickel-aluminum alloy metal product. In these particular alloys the high degree of porosity develops due to interdiifusion of nickel and aluminum at different rates. Where aluminum powder has been blended with a dispersion-modified nickel alloy, and the blended powders are compacted and subsequently heattreated for hot or cold working, non-thoriated areas appear in the areas where the original aluminum powder particles were present in the powder mix.

An object of this invention is to provide a process for producing an alloy comprising aluminum and iron, cobalt or nickel, in which alloy there is present a uniform dispersion of a refractory metal oxide, and which alloy after Working shows substantially no porosity in the finished work-piece. Another object is to produce intermediate metal work-pieces consisting of dispersion-modified nickelaluminum alloys, said intermediate products being suitable for further hot or cold-working steps to produce dispersion-modified aluminum-bearing mill products which exhi'bit little or no porosity due to interdifl'usion. Further objects will appear hereinbelow.

Now according to the present invention it has been found that the above-described difliculties of the prior methods for alloying aluminum with dispersion-modified metals of the iron group can be overcome, and non-porous mill products can be produced by powder blending the dispersion-modified iron-group metal or alloy with pow- 3,397,979 Patented Aug. 20, 1968 dered aluminum, if there is dispersed in the aluminum powder prior to or during the powder-blending step, about from 0.05 to 10% by volume of a particulate metal oxide having a AP at 1000 C. of at least 104 kilocalories per gram of oxygen and an average particle size in the range of 5 to millimicrons, compacting the mixture to a compact, sintering the compact, and hot or cold working the sintered compact.

The refractory oxides which are useful in the alloys of this invention will be those having free energy of formation (AF at 1000 C.) of at least 104 kilocalories per gram atom of oxygen. A typical group of suitable oxides, and their free energies of formation in kilocalories per gram atom of oxygen are shown in the following table:

In a preferred embodiment of the invention, fine particles of thoria are dispersed in elemental aluminum, and this dispersion-modified aluminum is alloyed with previously prepared dispersion-modified nickel.

The following example will illustrate the process of this invention:

Example A dispersion-modified nickel powder, known commer cially as TD nickel, produced by E. I. du Pont de Nemours and Company, having a particle size of '325 mesh, was blended with high purity (99.95%) aluminum powder and thoria'powder in the proportion of 93.6 wt. percent Ni alloy to 6 wt. percent Al to 0.4 wt. percent ThO The TD nickel powder was made by coprecipitating thoria particles and basic nickel carbonate, calcining the carbonate to hydrous nickel oxide, and reducing this oxide with hydrogen. The powder contained about 2% thoria as uniformly dispersed particles having an average size of about 25 millimicrons.

The three powders were blended in a double cone blender for 2 hours and the mixture then placed in a nickel ball mill with nickel balls and milled for approximately 8 hours. The powder mixture thus formed was compacted hydrostatically at 60,000 psi. The green compact was machined and canned in a mild steel container.

The canned compact was evacuated to a pressure of 5 microns to remove adsorbed air. During this evacuation, the compact was heated to approximately 200 F. The billet was then heated in hydrogen according to the following schedule:

2 hours at 600 F. 20 hours at 1150 F. 2 hours at 1650" F.

Following this heating, the billet was cooled in an atmosphere of hydrogen.

This sintered compact was extruded at a ratio of 8:1 at 1700 F. It was then subjected to a heat treatment at 2200 F. to homogenize it. During this heat treatment, gross porosity developed throughout the billet. The pores developed at the interface between the original TD nickel particles and the original aluminum particle due to interdifiusion of the nickel and aluminum particles. The diameter of the pores resulting from this interdiffusion varied from 1 to 25 microns and many times were interconnected so as to form cracks in the billet.

The extruded and heat-treated rod was hot swaged 30% at a temperature of 2000 F., and then was annealed at 2200 F. for two hours and water quenched. This hot-working step tended to make uniform the grain structure, since large grains occurred where the original aluminium particles were located, and fine grains occurred where the original TD nickel particles were located.

The annealed product was cold swaged 70% and following this cold-working step, the voids which had appeared in the billet prior to this step appeared to have collapsed and closed as was evidenced by fine dark lines in the microstructure.

The billet was heat-treated at 1850 F. for 2 hours. The effect of this heat treatment was to sinter the walls of the collapsed pores so that a metallurgical bond formed between the walls which had defined the void, and porosity in the rod was almost completely eliminated.

In the process described in the example, the ball-milling of the thoria powder, elemental aluminum powder, and dispersion-modified nickel powder results in the embedding of the thoria in the aluminum powder, and this dispersion-modified aluminum powder is concurrently and thoroughly mixed with the particles of diepersion-modified nickel. It is essential that the thoria be dispersed in the aluminum before the aluminum is alloyed with the dispersion-modified nickel by the steps of compaction, heating, and working; however, the example illustrates only one method by which this dispersion of the thoria in the aluminum can be accomplished, and other procedures can be used. For example, elemental aluminum powder and thoria can be ball-milled in a separate operation, and the resulting dispersion-modified aluminum thoroughly blended with dispersion-modified nickel before compacting, heating, and working to effect complete alloying.

Although in the example the dispersion-modified nickel alloy used was that known commercially as TD nickel, it is not intended that the claims be limited to the use of dispersion-modified iron, cobalt or nickel, or their alloys made by any particular process. The invention is conceived broadly to apply to the production of non-porous aluminum-bearing dispersion-modified iron group metals and alloys regardless of the process by which the oxide strengthening-agent is dispersed in the iron, cobalt, or nickel, or alloys; and also regardless of the particular method by which the strengthening refractory-metal oxide is incorporated in the elemental aluminum prior to the alloying step.

I claim:

1. In a process for alloying with aluminum an irongroup metal selected from the group consisting of iron, cobalt, nickel and alloys comprising these, said iron-group metal or alloy having dispersed substantially uniformly therein about from 0.05 to 10% by volume of a particulate metal oxide having a free energy of formation (AF) at 1000 C. of at least 104 kilocalories per gram atom of oxygen and an average particle size in the range of 5 to 100 millimicrons, the improvement which comprises the steps of (1) dispersing in particulate aluminum about from 0.05 to 10% by volume of a particulate metal oxide have a AF at 1000 C. of at least 104 kilocalories per gram atom of oxygen, (2) mixing a minor proportion of said oxide-containing aluminum with a major proportion of said dispersion-modified iron-group metal or alloy in particulate form, and (3) thereafter alloying the mixture by compacting, sintering and working.

2. A process of claim 1 in which the iron-group metal is nickel, the refractory oxide dispersed therein is thoria, and the oxide dispersed in the aluminum is also thoria.